On use, many electric components generate heat. For proper functioning of the electric component, it is necessary to remove the heat from the component. For heat removal, a number of heat conductive materials have been proposed. See JP-A 2000-63872, JP-A 2000-63873, JP-A 2000-109373, JP-A 2000-114438, JP-A 2000-129160, and JP-A 2003-301189.
The heat conductive materials generally take two forms, a sheet form which is easy to handle and a paste form commonly known as heat dissipating grease. While the heat dissipating grease suffers from a problem of cumbersome handling, one approach for overcoming the problem is to fill a syringe with the grease so that the grease may be applied by a dispensing machine. When it is desired to apply the grease to a member having a relatively large area, a printing technique using a metal screen or stencil is more efficient and accurate in applying the grease than the dispensing machine. The printing technique uses a squeegee in combination with a metal plate of stainless steel or the like having a desired pattern cut out. By moving the squeegee, the heat-dissipating grease is spread over the metal plate and thus coated onto a heat sink or similar member. The coating operation becomes difficult as the grease increases its viscosity.
The pursuit of the heat conduction capability of heat-dissipating grease leads to an increased loading of heat conductive filler in grease, resulting in grease with a higher viscosity. As a solution to this problem, it was already proposed to dilute a highly heat conductive silicone grease with a volatile solvent (see JP-A 2005-154532). However, it is understood as a matter of course that if the solvent volatilizes off prior to use, the grease experiences a rapid buildup of viscosity to such an extent to hinder screen printing. Differently stated, there is a strong likelihood that the grease ceases to exert its coating feasibility if the grease is stored for a long period over its expiration date, or if the container is opened and closed many times because the full content cannot be consumed at a time, or at worst, if the container is kept open for a long time until the content is used up. In fact, a laboratory follow-up test using a container filled with the heat-dissipating silicone grease composition of JP-A 2005-154532 demonstrated that when the lid of the container was kept open for 15 days at room temperature, the silicone grease increased its viscosity to such a level as to interfere with coating and working operation.
From the working standpoint, there is a need to have a heat-dissipating silicone grease composition which experiences no or little viscosity buildup even when the lid of the container is kept open at room temperature.